Various implantable medical devices (IMDs) may be used for therapeutically treating or monitoring one or more physiological conditions of a patient. Such IMDs may be adapted to monitor or treat conditions or functions relating to heart, blood vessels, muscle, nerve, brain, stomach, endocrine organs or other organs and their related functions. Advances in design and manufacture of miniaturized IMDs have resulted in IMDs capable of therapeutic as well as diagnostic functions, such as pacemakers, cardioverters, defibrillators, biochemical sensors, pressure sensors, various endovascular IMDs, and the like. Such IMDs may have electronic functions and may be wireless, with the ability to transmit data electronically either to another IMD implanted in the patient or to another device located externally of the patient, or both. IMDs with electronic functions may be coupled to electrical leads for delivering stimulation and sensing physiological parameters of the patient, catheters for delivering a substance, or may be leadless or catheterless. IMDs with electronic functions may include electrodes or sensors formed on, integral with, or within a housing of the IMD. Other IMDs may have purely mechanical and/or pharmaceutical functions, such as stents.
IMDs may include electrodes that provide one or more functions such as stimulation, sensing and/or other functionality. In various examples, an electrode may be distinct component of an IMD or a conductive housing of an IMD may also serve as an electrode. As another example, a conductive fixation mechanism for the IMD, such as a helical coil, may also serve as an electrode.